Their competence:

Are they a member of a trade or professional body? (e.g. the Arboricultural Association, International Society of Arboriculture, Forestry Contracting Association)

What is their safety performance like? (e.g. accident records)?

Can they provide examples of methods of work, risk assessments or other documentation to show they are familiar with the type of work?

Their management arrangements:

What are their procedures for managing health and safety?

Do they properly plan and organise work at height? (e.g. use of MEWP v climbing)

Will the work be sub-contracted and if so, how will they control it?

How do they supervise and manage their site work?

What Codes of Practice or standards will the contractor be working to e.g. AFAG safety guides, Guide to good climbing practice

Do they provide employees with the correct personal protective equipment? How do they monitor and check their own safety standards?

How do they inspect and check their equipment (owned or hired) e.g. as required by the Lifting Operations and Lifting Equipment Regulations

Do they have employers' liability, public liability and professional indemnity insurance?

Are they asking you about your risks or needs?

The more complex and potentially dangerous the activities, the more likely it is that the answers and information will need to be recorded. As the client, you will be responsible for checking that any contractor you appoint is competent to do the work safely.

Once you have selected a competent contractor, you will need to exchange information and agree the method of work. Both will need to be done before work starts. Pre-work meetings are a good way of ensuring that the work is properly planned and controlled. Finally, you will also need to monitor the work.